Television receiving device



June 6, 1950 s. WIKKENHAUSER 2,510,846

TELEVISION RECEIVING DEVICE Filed April 19, 1946 Gm Z'aq Witicenhaugez;

GMQAJM W W Patented June 6, 1950 TELEVISION RECEIVING DEVICE GustavWikkenhauser, Wells, England, assignor to Scophony Corporation ofAmerica, New York, N. Y., a corporation of Delaware Application April19, 1946, Serial No. 663,383 In Great Britain May 23, 1945 7 Claims.

This invention relates to television receiving devices of the type inwhich there is provided a constant light source combined with meansresponsive to received image contents signals for modulating the amountof light from said light source which is allowed to reach the finalimage screen. Various devices of this kind have been suggested in recentyears the independence of the modulation from the actual light sourcebeing a desirable feature particularly in connection with large screentelevision where high light intensity is vital. The invention thereforerelates particularly, though not exclusively, to devices for largescreen television.

The type of receiving devices with which the present invention isconcerned is further one in which the light modulating means comprise acathode ray tube having a deformable body adapted to be scanned over onesurface thereof by the cathode ray and so constituted and arranged thatelemental areas of a surface thereof are deformed in accordance with thereceived image contents signals corresponding to those elemental areas.The deformable body is so disposed in the light path between the lightsource and the image screen that the intensity of the light reaching thescreen is dependent upon the deformations of the said elemental areas.

In one device of this type described in United States Patent No.2,391,450 or in British patent specification No. 543,485 the deformablebody is in the form of a thin transparent membrane of a substance, suchas a gum or synthetic resin, having a low modulus of elasticity. Uponthe surface of this membrane which is scanned by the cathode ray aredistributed a large number of very small, mutually insulated metalplates and on the opposite surface of the membrane is a grid-likeelectrode composed of a number of rods at least equal to the number oflines in which the television picture is scanned. The metal plates arereflecting on the side thereof opposite to that scanned by the cathoderay. In operation electrostatic forces corresponding to the receivedimage signals are caused to act between the metal plates and thegrid-like electrode and produce deformations in the membrane. It isarranged that in the absence of such deformations substantially all thelight from the source, after reflection at the reflecting surfaces ofthe metal plates,

falls upon a mirror, suitablyarranged in the light path, but thatdeformation of the elemental areas of the membrane allow light to passthe mirror and reach the image screen. In a modification of the abovearrangement, also described in said patents, the grid-like electrode isreplaced by a transparent, homogeneous electrode, the light being inthis case transmitted through the membrane, the elemental surface ofwhich when deformed constitutes lenses which allow more or less light tobe reflected by the mirror and reach the image screen. In some cases themetal plates can be dispensed with and their function performed byelectrostatic charges built up on the scanned surface membrane.

The present invention is concerned exclusively with receiving devices ofthe type set forth in which the light in its path from the source to theimage screen is reflected at the surface of the deformable body and hasfor its object to provide a device of this type having improvedefficiency.

According to the present invention, in a television receiving device ofthe type set forth, the said deformable body is provided, upon thesurface thereof opposite to that scanned by the cathode ray, with asubstantially uniform and highly reflecting layer of metal, the saidmetal layer being disposed in the path of light from the said Iightsource to the said final image screen and the arrangement being suchthat when elemental areas of this metal layer are deformed in accordancewith received signals, the light reflected by these elemental areas onto the image screen is correspondingly varied in intensity. Thedeformable body is preferably of a solid material and the metal layer ismade as fiat as possible in the absence of deformation. The metal 1ayershould be so thin as not to interfere substantially with the deformationof the deformable body.

The light reflected from the metal layer does not pass through thedeformable body which may therefore be opaque if desired. The metalplates previously referred to, if provided, on the scanned surface ofthe body are not in the light path and therefore have no scatteringeffect on the light.

In order to obtain satisfactory contrast it will probably be necessaryto arrange that maximum light intensity on the image screen is producedwhen the elemental areas of the deformable body have maximumdeformation.

There may be provided in the light path a fixed mirror or other stop ordiaphragm which intercepts substantially all the light when noillumination of the image screen is required, and light may be arrangedto reach the screen either by spreading and passing around the outeredge of the mirror or stop or by contracting and passing through anaperture in the mirror or diaphragm.

The invention will be described by way of example with reference to theaccompanying drawing which illustrates diagrammatically one embodimentof the invention.

In the drawing there is shown a cathode ray tube I having a cathode H,control electrode 12, accelerating electrodes i3 and I4 anda screen 5.The electrodes are maintained-at suitable potentials by any convenientmeans such as a potential divider [3 connected to a suitable voltagesource. Two pairs of deflecting plates El and 18 are provided wherebythe cathode ray can-becaused to scan the screen 15.

The screen it comprises a deformable body-of insulating material l9having upon its scannedsurface a mosaic of conducting andmutuallyinsulated particles Zii. On the opposite sideof the body It is asubstantially uniform metal layer 21 which is highly reflecting. It isto be notedthatw.

in practice the body i9 will be very thin and is shown relatively,thicl; only for. the-sake of clear-,-

nesss A field lens 22 is supported -.-:within the envelope.

Light :from a source 23 is directed=bya lens 24irand a concave'mirror 25.uponthe, fieldlens- 22;;.';The;:reflecting layer '2! is arranged to besubstantially .flat 'in rthe absence of distortion i of sthe;:b.0dy:l9,-and under these conditions the light from the source :23 is reflected atthe layer 2! back through the-lens '22 onto the mirror 25.

When elemental" areasrof the surface 21 are dis-- torted',-'as.willbedescribed later, -however,-- light from theseareasypasses around :themirror 25 and is focusedsbyzalens ZBona final'imagescreen-Zl.

The distortion of the deformable;body i9, and

hence of "therefiecting layer :21,- in accordancewith received imagecontents signals may be e1"-- rooted in :a variety-50f awaysr." For[instance use may; bezmade' of secondary remission froni ythesoannedesurfaoe of the cmosaic-Zt in order to stabilise:the-potential;0f thezparticles thereof at a value'at which'thenumbercfprimary electrons reachingsa-particleirom the cathode ray is' equal tothe number. of secondary electrons emitted by the particle as a resultof the bombardment thereof i by the catho'devrayn In this case the imagesignals :Lmay zbe appliedacrossuanimpedance 28 r and serve tovarytheipotentialiof themetallayer 2h An electrode such as a conductingcoating-i 29*:dn thehwall of the GIIVGIODGJOIE the tube ti l;

ora grid maintained atta suitablfizotential, 'is

provided to collect'thesecondary electrons;

At anyinstant, in the absence of scanningr'when the imagesignalimpressesa given potential on theimetal layer 2!anzequahpotential'is' induced on the particles of the mosaic 2UOWlIlg:1tO"the,..

capacity-between the-particles 'a-ndthe metal lay.-

er there is therefore :no 'electrostatic' stress andhencenodeformation'of the body. 1 However when scanning is takingplaoa;each particle, as it is scanned, has its potential: brought .to thevalue above. referred to; andzwhenthis differs from the potential" onthe: metal. layer' 2 i ,ian electrostatic stresswill be set up in thebody. E9 in the region of. the particle beingescanned, This gives riseto" local-deformation of the body and of the metal with the result thatlightfrom this elemental area of :th metal. refiectinglayer passes themirror 25 'andr'eaches the'screen 21." It is to be noted that: :if theinsulation of the particles of the mosaic 20 is sufficientlyihiglras isdesirable, the

charge onieach particle will 'substantially'remain untilzthatparticlezis again scanned by the cathodeqrayr: Thus atrany, instantall.the'elemental' reflecting; surfaces constituting the :metalv layerv 4will have deformations corresponding to the image signals present whentheir corresponding particles were last scanned.

Although it is preferred that maximum i1lumination of the screen 21should correspond with maximum distortion of the metal layer it, as inthe exampleabove described this-is notv essential. If desired an annularmirror:.may.--be used as a diaphragm instead of the mirror 25 which actsas a, stop. In this case maximum illumination will correspond to minimumdistortion of the layer 2| and the sense of the image signals must beinverted. 1

Another way of causing variations of distortion of the body itcorresponding with image signals is to modulate the cathode ray withsuch signals, thelayer 2! being then maintained at a fixed potential andthe impedance 28 being usually replaced by .a direct connection.

For example velocity modulation may be used, the ;-velocity of the.electrons-=reaching .the mosaic ferences.=

Analternative way of operating ment is to apply the imag ,nais

he arrangw a an - it 1-1.- ped'ance 343 to the. control-electrode i2it]. ereby varyingrthe intensity of thevcathode ray beamz. In.theearlier:examplestheimpedanse would, 7 be -,replaced by a shortcircuits-In ithe present Y example.theznetal layerefiI maintainedat afixed -potentia1'..--The=velocityrofxthe bea nis 1-- ranged to be suchthat- 'secondary e negligible and the particles; theref tensit aofthe-impinging beam.

In this :casethe spaces "between the particles may be' rendered slightlywonductive in order to enabletthe charge acquired in'one'scantodissipate before the 'next"fscan.= The slightly [conductive coatin -maybe connected to point',

of suitable fixed potential.

The materialof thedeformable body should preferably have a highdielectric constant, and a high; breakdown strength'so that highvoltages: :canbe-maintained across-it without :leur ofbrealcdown.

A suitablev material for the'deformablebody:

er the namev [9 is polyeth'ylenesuoh-as is sold: 11nd polythene and'theconducting par scanned sidezii andthe reflecting; met

onitheopposite side of the body may be of silver. A foilaof polythenemay be stretched on. a fiat base, such as a glass; 'plate and a silverdeposit suitable-to act as the reflecting layer produced on one side rby well-known chemical silveringmethods; The foil'is'thenreversed andafurther deposit of silver is producedvby'theeame method on the oppositesurface. The latter-surface is then treated to subdivide thelconductinsuria-ce for example by placing the foil o'na flat base'andtrubbing thesilver .away along :two mutually;

perpendicular sets of "regularly spacednparallel linesusinga-xrulingxmachinerand: a' well rounded-1 e, na scanned, become morenegative I. with the Y in--.-

point under very light pressure to avoid injury to the polythene.

Any other known or suitable method of forming the mosaic 20 of mutuallyinsulated conducting particles may be employed. For instance the metalmay be evaporated on to the foil through a. grid. Alternatively twointersecting sets of parallel lines may be printed on to a surfaceof thefoil with a greasy paint or ink, the surface being then silvered and thesilver depositing only where the foil surface is not greasy. The surfaceis then washed with a solvent which dissolves and removes the paint orink.

When slight conductivity is to be given to the mosaic surface, thissurface may be sprayed or otherwise treated with a. suspension ofgraphite in water or other suitable liquid.

I claim:

1. An image reproducing device comprising a sealed envelope containing asource of electrons, a screen, means for directing said electrons in afine beam upon said screen and means for causing said beam to scan saidscreen, said screen comprising a. deformable body having on the scannedsurface thereof a mosaic of particles of conductivity high compared withthat of the spaces between them and having on the opposite surfacethereof an imperforate, flexible, light reflecting metal layer, and saidmetal layer being positioned to be capable of receiving light directedthereupon from outside said envelope and of reflecting said lightoutwards through said envelope.

2. A device according to claim 1, wherein said deformable body is aflexible foil of electrically insulating material.

3. A device according to claim 1, including means connected to saidlight reflecting layer for applying voltage thereto from outside saidenvelope.

4. A screen for use in television comprising a body deformable byreceived image contents signals, an imperforate, flexible, highly lightreflecting layer of conducting material on one surface of said body, andon the opposite surface a mosaic of particles of a conductivity highcompared with that of the spaces between them.

5. A screen such as described in claim 4 in which the deformable body isa flexible foil of electrically insulating material.

6. A screen such as described in claim 4 in which the deformable body isa flexible foil of polyethylene.

7. A screen such as described in claim 4 in which the light reflectinglayer and the mosaic particles are silver.

GUSTAV WIKKENHAUSER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,391,450 Fischer Dec. 25, 1945FOREIGN PATENTS Number Country Date 539,496 Great Britain Sept. 12, 1941OTHER REFERENCES Ser. No. 354,771, Paehr (A. P. 0.), published May 18,1943.

Ser. No. 428,973, De France (A. P. 0.), published July 15, 1943.

